use anyhow::Result;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use tracing::info;

/// Data analyzer for automated database analysis
#[derive(Debug)]
pub struct DataAnalyzer {
    // Configuration and state
}

/// Analysis result structure
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AnalysisResult {
    pub summary: String,
    pub insights: Vec<Insight>,
    pub recommendations: Vec<Recommendation>,
    pub performance_metrics: PerformanceMetrics,
}

/// Data insight
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Insight {
    pub title: String,
    pub description: String,
    pub severity: InsightSeverity,
    pub category: InsightCategory,
}

/// Insight severity levels
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum InsightSeverity {
    Info,
    Warning,
    Critical,
}

/// Insight categories
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum InsightCategory {
    Performance,
    DataQuality,
    Security,
    Schema,
    Usage,
}

/// Recommendation for improvement
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Recommendation {
    pub title: String,
    pub description: String,
    pub impact: RecommendationImpact,
    pub effort: RecommendationEffort,
    pub sql_example: Option<String>,
}

/// Recommendation impact levels
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum RecommendationImpact {
    Low,
    Medium,
    High,
}

/// Recommendation effort levels
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum RecommendationEffort {
    Low,
    Medium,
    High,
}

/// Performance metrics
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PerformanceMetrics {
    pub execution_time_ms: f64,
    pub rows_examined: Option<u64>,
    pub rows_returned: Option<u64>,
    pub index_usage: HashMap<String, bool>,
    pub query_complexity: QueryComplexity,
}

/// Query complexity levels
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum QueryComplexity {
    Simple,
    Moderate,
    Complex,
    VeryComplex,
}

impl DataAnalyzer {
    /// Create a new data analyzer
    pub fn new() -> Self {
        Self {}
    }
    
    /// Analyze a SQL query for performance and optimization opportunities
    pub async fn analyze_query(&self, sql: &str) -> Result<AnalysisResult> {
        info!("Analyzing SQL query for performance");
        
        // TODO: Implement actual query analysis
        // This is a placeholder implementation
        
        let complexity = self.assess_query_complexity(sql);
        let insights = self.generate_insights(sql);
        let recommendations = self.generate_recommendations(sql);
        
        let performance_metrics = PerformanceMetrics {
            execution_time_ms: 150.0, // Placeholder
            rows_examined: Some(1000),
            rows_returned: Some(10),
            index_usage: HashMap::new(),
            query_complexity: complexity,
        };
        
        Ok(AnalysisResult {
            summary: format!("Analysis completed for query with {} characters", sql.len()),
            insights,
            recommendations,
            performance_metrics,
        })
    }
    
    /// Analyze data quality in a table
    pub async fn analyze_data_quality(&self, table_name: &str) -> Result<AnalysisResult> {
        info!("Analyzing data quality for table: {}", table_name);
        
        // TODO: Implement actual data quality analysis
        // This is a placeholder implementation
        
        let insights = vec![
            Insight {
                title: "Null Values Detected".to_string(),
                description: format!("Table {} contains null values in critical columns", table_name),
                severity: InsightSeverity::Warning,
                category: InsightCategory::DataQuality,
            }
        ];
        
        let recommendations = vec![
            Recommendation {
                title: "Add NOT NULL Constraints".to_string(),
                description: "Consider adding NOT NULL constraints to critical columns".to_string(),
                impact: RecommendationImpact::Medium,
                effort: RecommendationEffort::Low,
                sql_example: Some(format!("ALTER TABLE {} MODIFY COLUMN name NOT NULL;", table_name)),
            }
        ];
        
        Ok(AnalysisResult {
            summary: format!("Data quality analysis for table {}", table_name),
            insights,
            recommendations,
            performance_metrics: PerformanceMetrics {
                execution_time_ms: 50.0,
                rows_examined: None,
                rows_returned: None,
                index_usage: HashMap::new(),
                query_complexity: QueryComplexity::Simple,
            },
        })
    }
    
    /// Assess the complexity of a SQL query
    fn assess_query_complexity(&self, sql: &str) -> QueryComplexity {
        let sql_lower = sql.to_lowercase();
        let mut complexity_score = 0;
        
        // Count complexity indicators
        if sql_lower.contains("join") { complexity_score += 1; }
        if sql_lower.contains("subquery") || sql_lower.contains("select") && sql_lower.matches("select").count() > 1 { complexity_score += 2; }
        if sql_lower.contains("union") { complexity_score += 1; }
        if sql_lower.contains("group by") { complexity_score += 1; }
        if sql_lower.contains("having") { complexity_score += 1; }
        if sql_lower.contains("order by") { complexity_score += 1; }
        if sql_lower.contains("window") || sql_lower.contains("over(") { complexity_score += 2; }
        
        match complexity_score {
            0..=1 => QueryComplexity::Simple,
            2..=3 => QueryComplexity::Moderate,
            4..=6 => QueryComplexity::Complex,
            _ => QueryComplexity::VeryComplex,
        }
    }
    
    /// Generate insights based on SQL analysis
    fn generate_insights(&self, sql: &str) -> Vec<Insight> {
        let mut insights = Vec::new();
        let sql_lower = sql.to_lowercase();
        
        // Check for SELECT *
        if sql_lower.contains("select *") {
            insights.push(Insight {
                title: "SELECT * Usage".to_string(),
                description: "Using SELECT * can impact performance and maintainability".to_string(),
                severity: InsightSeverity::Warning,
                category: InsightCategory::Performance,
            });
        }
        
        // Check for missing WHERE clause
        if sql_lower.contains("select") && !sql_lower.contains("where") && !sql_lower.contains("limit") {
            insights.push(Insight {
                title: "Missing WHERE Clause".to_string(),
                description: "Query may return more data than necessary".to_string(),
                severity: InsightSeverity::Info,
                category: InsightCategory::Performance,
            });
        }
        
        insights
    }
    
    /// Generate recommendations based on SQL analysis
    fn generate_recommendations(&self, sql: &str) -> Vec<Recommendation> {
        let mut recommendations = Vec::new();
        let sql_lower = sql.to_lowercase();
        
        // Recommend specific columns instead of SELECT *
        if sql_lower.contains("select *") {
            recommendations.push(Recommendation {
                title: "Specify Column Names".to_string(),
                description: "Replace SELECT * with specific column names for better performance".to_string(),
                impact: RecommendationImpact::Medium,
                effort: RecommendationEffort::Low,
                sql_example: Some("SELECT id, name, email FROM users;".to_string()),
            });
        }
        
        // Recommend adding LIMIT clause
        if sql_lower.contains("select") && !sql_lower.contains("limit") {
            recommendations.push(Recommendation {
                title: "Add LIMIT Clause".to_string(),
                description: "Consider adding a LIMIT clause to prevent large result sets".to_string(),
                impact: RecommendationImpact::High,
                effort: RecommendationEffort::Low,
                sql_example: Some("SELECT * FROM users LIMIT 100;".to_string()),
            });
        }
        
        recommendations
    }
}

impl Default for DataAnalyzer {
    fn default() -> Self {
        Self::new()
    }
}
